Noise control constitutes a rapidly growing economic and public policy concern for the construction industry. Areas with high acoustical isolation (commonly referred to as ‘soundproofed’) are requested and required for a variety of purposes. Apartments, condominiums, hotels, schools and hospitals all require walls, ceilings and floors that are specifically designed to reduce the transmission of sound in order to minimize or eliminate the disruption to people in adjacent rooms. Soundproofing is particularly important in buildings adjacent to public transportation including highways, airports and railroad lines. Additionally, theaters and home theaters, music practice rooms, recording studios and others require increased noise abatement for acceptable listening levels. Likewise, hospitals and general healthcare facilities have begun to recognize acoustical comfort as an important part of a patient's recovery time. One measure of the severity of multi-party residential and commercial noise control issues is the widespread emergence of model building codes and design guidelines that specify minimum Sound Transmission Class (STC) ratings for specific wall structures within a building. Another measure is the broad emergence of litigation between homeowners and builders over the issue of unacceptable noise levels. To the detriment of the U.S. economy, both problems have resulted in major builders refusing to build homes, condos and apartments in certain municipalities; and in cancellation of liability insurance for builders.
Various construction techniques and products have emerged to address the problem of noise control, such as: replacement of wooden framing studs with light gauge steel studs; alternative framing techniques such as staggered-stud and double-stud construction; additional gypsum drywall layers; the addition of resilient channels to offset and isolate drywall panels from framing studs; the addition of mass-loaded vinyl barriers; cellulose-based sound board; and the use of cellulose and fiberglass batt insulation in walls not requiring thermal control. All of these changes help reduce the noise transmission but not to such an extent that certain disturbing noises (e.g., those with significant low frequency content or high sound pressure levels) in a given room are prevented from being transmitted to a room designed for privacy or comfort. The noise may come from rooms above or below the occupied space, or from an outdoor noise source. In fact, several of the above named methods only offer a three to six decibel improvement in acoustical performance over that of standard construction techniques with no regard to acoustical isolation. Such a small improvement represents a just noticeable difference, not a soundproofing solution. A second concern with the above named techniques is that each involves the burden of either additional (sometimes costly) construction materials or extra labor expense due to complicated designs and additional assembly steps.
More recently, an alternative building noise control product has been introduced to the market in the form of a laminated damped drywall panel as disclosed in U.S. Pat. No. 7,181,891. That panel replaces a traditional drywall layer and eliminates the need for additional materials such as resilient channels, mass loaded vinyl barriers, additional stud framing, and additional layers of drywall. The resulting system offers excellent acoustical performance improvements of up to 15 decibels in some cases. However, the panel cannot be cut by scribing and breaking. Rather than using a box cutter or utility knife to score the panel for fracture by hand, the panels must be scored multiple times and broken with great force over the edge of a table or workbench. Often times, the quality of the resulting break (in terms of accuracy of placement and overall straightness) is poor. The reason for the additional force required to fracture the laminated panel is because the component gypsum layers have a liner back paper (or liner fiberglass nonwoven) that has a high tensile strength. Tests have shown that scored panels of this type require approximately 85 pounds of force to fracture versus the 15 pounds required to break scored ½ inch thick standard gypsum wallboard and the 46 pounds of force required to break scored ⅝ inch thick type X gypsum wallboard. This internal layer (or layers, in some cases) must be broken under tension via considerable bending force during a typical score and snap operation.
In many cases, the tradesman is forced to cut each panel with a power tool such as a circular saw or a rotary cutting tool to ensure a straight cut and a high quality installation. This adds time and labor costs to the panel installation and generates copious amounts of dust which act as a nuisance to the laborers and adds even more installation expense in the form of jobsite clean up.
A figure of merit for the sound reducing qualities of a material or method of construction is the material or wall assembly's Sound Transmission Class (STC). The STC rating is a classification which is used in the architectural field to rate partitions, doors and windows for their effectiveness in blocking sound. The rating assigned to a particular partition design as a result of acoustical testing represents a best fit type of approach to a curve that establishes the STC value. The test is conducted in such a way as to make it independent of the test environment and yields a number for the partition only and not its surrounding structure or environment. The measurement methods that determine an STC rating are defined by the American Society of Testing and Materials (ASTM). They are ASTM E 90, “Standard Test Method Laboratory Measurement of Airborne Sound Transmission Loss of Building Partitions and Elements,” and ASTM E413 “Classification for Sound Insulation,” used to calculate STC ratings from the sound transmission loss data for a given structure. These standards are available on the Internet at www.astm.org.
A second figure of merit for the physical characteristics of construction panels is the material's flexural strength. This refers to the panel's ability to resist breaking when a force is applied to the center of a simply supported panel. Values of flexural strength are given in pounds of force (lbf) or Newtons (N). The measurement technique used to establish the flexural strength of gypsum wallboard or similar construction panels is ASTM C 473 “Standard Test Methods for the Physical Testing of Gypsum Panel Products”. This standard is available on the Internet at www.astm.org.
The desired flexural strength of a panel is dependant upon the situation. For a pristine panel, a high flexural strength is desirable since it allows for easy transportation and handling without panel breakage. However, when the panel is scored by the tradesman (for example, with a utility knife) for fitting and installation, a low flexural strength is desirable. In that case, a low value indicates that the scored panel may be easily fractured by hand without excessive force.
Accordingly, what is needed is a new material and a new method of construction to reduce the transmission of sound from a given room to an adjacent area while simultaneously minimizing the materials required and the cost of installation labor during construction.